The comorbid presence of trauma and substance misuse is becoming increasingly recognized as a common occurrence that causes significant functional impairment in clients, and presents numerous challenges to clinicians. The first chapter in this thesis reviews recent empirical and theoretical literature regarding the nature of the relationship between trauma and substance misuse so as to highlight principal considerations applicable to the process of conceptualisation. In addition, Chapter two presents results of a principal component analysis of the Beliefs About Substance Use inventory (BASU) in order to facilitate the accurate measurement of beliefs in individuals who misuse substances. Findings indicated that in addition to its overall score reflecting the extent of dysfunctional be1iefs about substance use, the BASU is also able to evaluate important beliefs with regard to motivations for continued use, barriers to cessation and withdrawal, beliefs about dependence whilst also addressing contemplative state. With a view to further enhancing current conceptual knowledge, findings from the main empirical paper focussing on the role of beliefs in the relationship between trauma and alcohol abuse, are presented in chapter three. Associations between trauma exposure, trauma symptom severity, negative posttraumatic cognitions, beliefs about substance use and drinking expectations were examined. Following this preliminary investigation, results highlighted the significant contribution of trauma symptom severity and negative posttraumatic cognitions in relation to beliefs and expectancies about alcohol.